This invention relates to processing communication satellite systems and more particularly relates to coordination between the uplinks and downlinks of such systems.
A multibeam processing satellite system requires a comprehensive and consistent approach to its transmission system, including both its uplink and its downlink. Since the uplink and downlink transmission systems are decoupled by the processing (by demodulation, decoding, and switching) on the satellite, these two parts may be defined separately. However, in order to obtain optimum performance, the uplink and downlink should be connected or coordinated to moderate the uplink transmission in accordance with downlink transmissions.
The uplink transmission system definition must include all aspects relating to the spatial, polarization, spectral, and temporal attributes and, in particular, methods of multiple access to permit many users to utilize the uplink concurrently. Additionally, various data handling issues, including error control and protocol aspects relating to the way that transmission data are organized, must be defined.
The downlink transmission system definition must include all aspects relating to the spatial, polarization, spectral, and temporal attributes and, in particular, methods of multiplexing to permit many users to be concurrently serviced by the downlink. Additionally, various data handling issues, including error control and protocol aspects relating to the way that transmission data units are organized must be defined.
The coordination between uplink and downlink must be consistent with both the uplink transmission system definition and the downlink transmission system definition.
A first embodiment of the invention is useful in a processing satellite communication system comprising an uplink for transmitting uplink data cells on an uplink beam from a ground terminal to the satellite and a downlink for transmitting downlink data cells on a downlink beam from the satellite to a ground terminal. The first embodiment may be used for controlling the transmission of the uplink data cells. In such an environment, the uplink data cells are grouped with an error correction code, preferably by an encoder. The uplink data cells also are located in predetermined uplink time slots within uplink frames comprising the uplink data cells. The uplink frames are modulated by a predetermined form of modulation to enable placement of the modulated uplink frames into a plurality of uplink channels suitable for transmission to the satellite on the uplink beam. The uplink channels comprise a plurality of the uplink time slots, and the modulating preferably is done by a modulator. The power level at which the uplink beam may be transmitted to the satellite is made adjustable, preferably by using an adjustable amplifier. The channels are demodulated into demodulated uplink frames, preferably by a demodulator located at the satellite. The error correction code is decoded, errors in the correction code are detected and at least an error estimate of errors in said correction code is made, preferably by a decoder located at the satellite. Report cells are formed comprising error information in response to the error estimate, addresses identifying destinations and identifiers indicating that the report cells contain the error information. The report cell forming preferably is done with a cell former located in the satellite. Downlink frames comprising the report cells are generated for transmission on the downlink beam, preferably by a frame organizer located in the satellite. The report cells from the downlink frames are unpacked and the power level is adjusted based on the error information in the report cells, preferably by a processor responsive to the downlink beam located at one of the ground terminals.
A second embodiment of the invention also is useful in a processing satellite communication system comprising an uplink for transmitting uplink data cells on an uplink beam from a ground terminal to the satellite and a downlink for transmitting downlink data cells on a downlink beam from the satellite to a ground terminal. The second embodiment also may be to used for controlling the transmission of the uplink data cells. In such an environment, burst signals are located or placed in predetermined time slots within uplink frames comprising the uplink data cells, preferably by an uplink frame organizer located at the ground terminal.
The uplink frames are launched at a predetermined adjustable time from the ground terminal so as to place the uplink frames into a plurality of uplink channels suitable for transmission to the satellite on the uplink beam. The uplink channels comprise a plurality of the time slots. The launching preferably is done with an uplink unit located at the ground terminal. The power level at which the uplink beam may be transmitted to the satellite is made adjustable, preferably by using an adjustable amplifier located at the ground terminal. The channels are demodulated into demodulated uplink frames, preferably by a demodulator located at the satellite. At least an estimate of the received energy of the burst signals or the time of arrival of the burst signals at the satellite is made, preferably by an uplink processor responsive to the uplink beam and located at the satellite. Report cells comprising report information in response to the estimate of the received energy of the burst signal or the time of arrival of the burst signal at the satellite, addresses identifying destinations and identifiers indicating that the report cells contain the report information are generated, preferably by a cell former located at the satellite. Downlink frames comprising the report cells are generated for transmission on the downlink beam, preferably by downlink frame organizer located at the satellite. The report cells are unpacked from the downlink frames, the power level is adjusted based on the report information in the report cells in response to the estimate of the received energy of the burst signal or the adjustable time is adjusted based on the report information in the report cells in response to the time of arrival of the burst signals at the satellite. The unpacking and adjustments preferably are made by a downlink processor responsive to the downlink beam and located at the ground terminal.
In summary, the preferred embodiments of the invention provide coordination between an uplink and a downlink that is highly efficient, versatile, and accurate.